Answer:
Option D
Explanation:
Germany, is the right answer.
On 18 January 1871, the Palace of Versailles in France witnessed the unification of Germany into the integrated nation (politically and administrative).
All the princes of German states assembled in the palace, except Austria, in order to declare or proclaim the William I of Prussia as the Emperor of Germany after the capitulation of French in the war of Franco-Prussian.
The de facto transition of German-speaking populations had helped the in the beginning of the Napoleonic war era and later which resulted in the dilution of Roman Empire in 1806. Therefore, option D (Germany) will be the right answer.